Ernst Kitzinger

Ernst Kitzinger, who has died aged 90, was one of the last distinguished art historians to flee 1930s Germany, and effectively changed the reputation of art history in the English-speaking world. His interests ranged over late antique and early medieval art - from Anglo-Saxon North- umbrian through Roman to Byzantine - a vast spectrum of expertise that enabled him to put a new shape to the way in which we understand the development of artistic practice in the first millennium.

He wrote searching analyses of the mosaics of the great churches of Norman Sicily, in effect his principal, lifelong project; on the imagery in the floor mosaics of early Christian churches, a previously neglected medium which provided great insights into how these buildings were thought of and used; on the icons of the early church and the phenomenon of iconoclasm; and, finally, a radical exposition of the shape and development of artistic practice and production over the two centuries spanning the final collapse of the Roman world system.

Kitzinger was born into a professional Jewish family in Munich. He studied at the city's university, completing his doctoral thesis at breakneck speed before arriving in England in 1935. His seminal study of painting and mosaics in Rome in the earliest middle ages remains a fundamental starting point for the study of early medieval art in Rome.

Alone in London, and with few resources, he was taken on by TD Kendrick, the spirited and far-sighted deputy curator of the British and medieval department at the British museum (he later became director), to join his study of the surviving remains of Anglo-Saxon art. The experience of touring northern England and southern Scotland with Kendrick gave Kitzinger an introduction to Anglo-Saxon sculpture and painting which was to remain with him.

His ability to see this material from a continental and Mediterranean context bore fruit in a number of still fundamental publications, on vine-scroll ornament and the remarkable wooden coffin of St Cuthbert in Durham. He was still at the museum when the great 7th-century ship burial at Sutton Hoo was excavated in 1939, and was responsible for the first assessment of the extraordinary assemblage of late Roman and early Byzantine silver plate at the site.

His most far-reaching achievement, however, was his book, Early Medieval Art At The British Museum (1940), a brilliant and best-selling introduction to the arts of the first millennium, based on the museum's collections. This work showed English readers new ways of looking and thinking, which reflected the concerns of advanced scholarship on the continent.

With the outbreak of war, Kitzinger was interned and evacuated to Australia. In 1941, he emigrated to the United States and joined the new centre for Byzantine studies at Dumbarton Oaks, in Washington, DC, where he stayed for 25 years, becoming director of studies and professor of Byzantine art and archaeology. Under his guidance, it became the world's leading institution for Byzantine studies.

In 1967, he moved to Harvard, where he turned his energies to teaching. In this, he was phenomenally successful. Always scrupulously respectful of others, he never tried to impose his beliefs and methods; his homes were always open and somehow almost innocently welcoming.

Although he never spent time in Austria, Kitzinger was really one of the last great exponents of what we think of as the Viennese tradition of art historical method, of Kunstwissenschaft. He believed in the primacy of the eye, and sought, in formal configurations and the touch of style, the essential channels of access to, and understanding of, the central motivations and mentality of a culture and an age. Trained in the skills of historical research and analysis, he also had an acute sense for the value of factual evidence.

A shy and retiring person, he was more at home in the study and the library than in the field. One look at the original was enough, and all his time and endeavour would be spent in contextual research, with texts and reproductions.

Kitzinger's eminence was widely recognised. As Slade professor of fine art at Cambridge University (1974-75), he delivered a series of lectures which were later published as Byzantine Art In The Making (1977), a book which made his ideas on the shape of artistic practice between Constantine and the outbreak of Byzantine iconoclasm accessible to a wide audience.

In Italy, too, he was held in high esteem. Quite early on, he also picked up old connections from his Munich days, and Germany made its own peace by enrolling him as a member of the order Pour Le Mérite, its highest accolade of academic recognition.

In retirement, he spent his time between Oxford and Princeton. In his 80s, at the rate of a volume a year, he wrote six volumes of plates with accompanying commentaries, which effectively completed his corpus of the Norman mosaics of Sicily. He had accomplished the seemingly impossible - publishing and elucidating all of the thousands of square feet of Sicilian wall mosaics.

His wife Susan, a Quaker and an artist, whom he married in 1944, died in 2000; he is survived by his children, Tony, Rachael and Adrian.

· Ernst Kitzinger, art historian, born December 27 1912; died January 22 2003